Looking at the photo it is easy to imagine why field-testing is needed to show whether an intervention is actually saving fuel. Real life is complicated and is not replicated in a lab.
The use of a Water Boiling Test to determine if new stoves are saving fuel has historically been questionable. WBT’s tend to underestimate fuel use compared to field tests. (Hernández, 2014; Teune et al., 2020, Bayer et al., 2013).
Water Boiling Tests are great for international stove comparisons when variables are controlled. WBTs are also useful to investigate how stoves might be improved and to experiment with iterative changes that could improve heat transfer and combustion efficiency.
Luckily, we were assured at ETHOS 2025 that only field tests would be used from now on to calculate fuel savings for carbon credits.
When data from field testing was replaced with lab-based results it was such an obvious mistake!
Of course, any type of testing needs to be done carefully by a third party.
https://aprovecho.org/wp-content/uploads/2025/07/5703178844_856986299e_c.jpg535800Kim Stillhttps://aprovecho.org/wp-content/uploads/2015/11/Aprovecho-Logo.pngKim Still2025-07-30 15:42:442025-07-30 15:42:45Carbon Credits and Fuel Savings?
In my opinion, the WBT* cannot be used, especially in the lab, to improve a biomass cook stove because all of the important field variables are not represented.
A successful cook stove needs to be evolved from field tests, as we did in Southern India for the Shell Foundation. Cooks in eighteen villages kept on changing the Rocket stove until it was acceptable, useful, and even likable. It took a while but it was a lot of fun and a great introduction to Southern India!
The WBT, with severely limited variables, can be useful in the lab for international comparisons of stove performance. The same pots, same amount of water, same fuel, same procedures and protocols limit the confounding variables in an attempt to isolate the stove as the reason for perceived differences.
As we did in India, both field and lab data can inform stakeholders. The successful stove has to please cooks, retailers, distributors, etc. and, at the same time, meet project goals such as reducing adverse health effects. We used the WBT in the lab and the CCT* in the field. Marketing tests, as suggested by Baldwin (1987) were very important, as well. We learned right away that the stove had to cost ~$5 to capture sustainable market share.
The lab based WBT is best used to inform researchers how stoves might be improved. Then, iterations in prototypes are tried in the field including cost, weight, color, height, firepower, fuel used, etc, etc.
This combined use of the WBT, CCT, and KPT* for stove development was suggested in the International Stove Standards, (1985).
*Water Boiling Test “The Water Boiling Test (WBT) is a simplified simulation of the cooking process. It is intended to measure how efficiently a stove uses fuel to heat water in a cooking pot and the quantity of emissions produced while cooking.” – The Water Boiling Test Version 4.2.3
*Controlled Cooking Test “The controlled cooking test (CCT) is designed to assess the performance of the improved stove relative to the common or traditional stoves that the improved model is meant to replace. Stoves are compared as they perform a standard cooking task that is closer to the actual cooking that local people do every day.” – CCT version 2.0
*Kitchen Performance Test “The Kitchen Performance Test (KPT) is the principal field–based procedure to demonstrate the effect of stove interventions on household fuel consumption.” -KPT version 3.0
Thanks to the Osprey Foundation, ARC just finished building a new heating stove lab and we are experimenting with how to make very clean burning home heating stoves. The intended price points are considerably lower than higher emission stoves currently for sale. Zero Green Premium products cost less than the dirty technology products they replace.
We change one variable at a time in a prototype and test the result under the emissions hood that collects and records the amounts of climate gases and Black Carbon. Usually ~50 iterations result in a closer to optimal stove. The new Osprey Health and Climate Heating Stove Lab is set up to do 3 to 6 iterations per week. Lab staff includes Travis Volpe who builds, tests and changes prototypes. The prototype is thoroughly field-tested, as well.
In the first week of October, ARC Research and Development Engineer Jaden Berger visited CSIR-Ghana for capacity building training. The Council for Scientific and Industrial Research (CSIR) is the foremost national science and technology institution in Ghana.
The main focus of the visit was to teach them how to perform field testing using various sensor suites. CSIR was especially focussed on learning to perform KPTs (Kitchen Performance Tests) while using EXACT sensors from Climate Solutions Consulting. We also used other sensors CSIR already had: a PEMS (Portable Emissions Monitoring System) with a portable hood, an IAP (Indoor Air Pollution) meter, and an air quality sensor along with performing UCETs (Uncontrolled Cooking Efficiency Tests) during cooking to determine the efficiency of the stove.
Making observations of how cooks are using stoves.
Setting up a PEMS with a portable hood to measure stove emissions.
Testing was done at a secondary boy’s boarding school in Accra. The school cooks breakfast, lunch, and dinner for 3,000 students using a variety of improved and unimproved stoves. The stoves identified as the least efficient and highest emitters were the 12 wood stoves and 4 palm kernel stoves. (Palm kernels used to be considered agricultural waste from palm oil production but are now commonly used as fuel.) Several design meetings were held to determine a design that would increase efficiency, clean up emissions, and remove emissions from the room the cooks were in.
Palm kernel stoves in use for breakfast.
Weighing wood for three 24 hour-long KPTs.
Performing UCET measurements.
The next step is for CSIR to finalize a CAD model of the design along with some CFD analysis to predict if the prototype will work. ARC will then virtually meet with CSIR and their manufacturer to finalize the design and begin creating prototypes.
During the second week of the visit, ARC and CSIR worked on wrapping up older projects. This included gathering final data for a charcoal conversion efficiency study, creating a draft of the charcoal conversion efficiency protocol so that it can be published, and developing and using a durability protocol that is more applicable to conditions a stove will have to withstand in Ghana.
Taking measurements for creating a new durability protocol.
Overall, a successful trip with good progress made toward improving health and cooking conditions in Ghana.
https://aprovecho.org/wp-content/uploads/2024/11/Screenshot-2024-11-07-at-4.18.41-PM.png358390Kim Stillhttps://aprovecho.org/wp-content/uploads/2015/11/Aprovecho-Logo.pngKim Still2024-11-07 16:01:042024-11-07 16:20:19ARC Assists CSIR-Ghana in Capacity-Building
I just returned to the Oregon lab from a two-week visit to Shengzhou Stove Manufacturer. The next few newsletters will be about SSM and progress made. There’s a lot to talk about! SSM has sold over 5 million stoves and the factory is a wonderful place to visit.
SSM started testing stoves for durability twenty-four hours a day (three eight hour shifts at a nearby farming community) three years ago. The farmers keep fires going in eight SSM stoves and the tests continue for one year of each stove. That’s 8, 860 hours.
It’s great that SSM has been doing long term, real life testing of their stoves. Previously, tests in a kiln with wet, salted pieces of metal resulted in confusing estimates of durability. In 2017, M.P. Brady and T.J. Theiss shocked the stove world by showing that in a wet, salty, hot kiln even very expensive metals were not long lasting. (Energy for Sustainable Development 37 (2017) 20–32, “Alloy Corrosion Considerations in Low-Cost, Clean Biomass Cookstoves for the Developing World”, Michael P. Brady, et al.).
The SSM testing is being written up. It seems to show much longer durability of various combustion chamber metals when real fires are used. Full details to follow.
https://aprovecho.org/wp-content/uploads/2024/08/PHOTO-2024-08-11-00-06-57.jpg8101080Kim Stillhttps://aprovecho.org/wp-content/uploads/2015/11/Aprovecho-Logo.pngKim Still2024-08-16 15:29:022024-08-16 15:29:42Durability Testing at SSM
Unfortunately, although introductions to lab tests warn that results do not predict actual performance, the recent use of lab data to earn carbon credits has made an unfortunate error more commonplace. For decades, introductions to lab tests have warned that only field-testing can determine actual efficiency, emissions, effectiveness, market validity, etc. The World Health Organization based their stove standards aimed at protecting health on field-testing for this reason.
Lab tests are helpful when comparing performance to understand how fire might be more useful.Starting with the 1985 International Standards, test users were advised not to use lab data to predict actual performance. While improving other carbon methodologies, using field-testing to estimate reductions would dramatically improve the accuracy of offsets.
Carefully performed lab tests tend to overestimate fuel efficiency and underestimate emissions. This has landed cook stoves and heating stoves in serious controversy. A lab tested Tier 4 cookstove can be Tier 2 in real life – or mistaken for a flowerpot. My first Rocket stoves were often used for this important function in Mexico.
A lab tested 2 g/hr PM heating stove often emits a lot more smoke when the harmful pollutant is measured from chimneys in houses. In an effort to reduce confounding variables, lab tests show closer to optimal performance. Real life human beings tend to operate stoves with less care, wood is wet, life deserves attention, too.
Maybe the test warnings should have been highlighted in green?
International Standards, 1985
“This is a laboratory test…while it does not necessarily correlate to actual stove performance, when cooking food, it facilitates the comparison of stoves under controlled conditions with relatively few cultural variations.” (Testing the Efficiency of Wood Burning Cookstoves, International Standards 1985).
(ISO 19867-1)
“This document provides a standard test sequence that can be used to compare the performance of various cookstove types, cookstove fuels, and cooking practices under controlled laboratory test conditions, as specified in this document. For evaluation of the performance and predicted outcomes of a cooking system in the field [comprising cookstove(s), fuel(s), cooking vessel(s), kitchen, ventilation, and user(s)], ISO 198691 applies.”
Since 2012, optimized biomass cook stoves have been tested at ~50% thermal efficiency
The temperature of the hot gases flowing past the surface of the pot is increased by
Creating as much flame (1,100C) as possible in a low mass, insulated combustion chamber.
Decreasing the distance between the fire and the pot without making excess smoke.
Not allowing external air to cool the combustion gasses.
In convective heat transfer, the primary resistance is the surface boundary layer of still air immediately adjacent to a wall.
Increasing Temperatures, increasing exposed Area, increasing Radiation, increasing Velocity in a 6mm to 7mm channel gap (10cm or higher) pot skirt has been shown (up to 5kW firepower) in a 24cm or larger diameter pot to result in ~50% thermal efficiency. Reducing losses from the exterior of the pot skirt with refractory ceramic fiber insulation also increases thermal efficiency.
60% thermal efficiency has been demonstrated in the lab.
https://aprovecho.org/wp-content/uploads/2024/03/image-1.png693995Kim Stillhttps://aprovecho.org/wp-content/uploads/2015/11/Aprovecho-Logo.pngKim Still2024-03-22 15:37:372024-03-22 15:39:47From: EPA’s Lab Test Results for Household Cookstoves, Jim Jetter, 2012
Most stoves that were tested had better thermal efficiency, but some did not.
Compared with the 3-stone fire, many stoves that were tested had better combustion efficiency, but many did not.
A natural-draft TLUD stove (ARC) had very high efficiency with processed, wood-pellet fuel with low-moisture content.
Some forced-draft (fan) stoves had very low emissions – but not all fan stoves did.
Most natural-draft stoves that were tested showed a bigger improvement (lower emissions) over the 3-stone fire with high moisture fuel than with low-moisture fuel.
A natural-draft TLUD stove (ARC) had very low emissions – but required processed, wood pellet fuel with low-moisture content.
Two rocket stoves were tested at a “medium power” level – and had lower emissions (per energy delivered to cooking pot) than at maximum power.
Charcoal stoves had high emissions of CO and high emissions of PM during start-up.
https://aprovecho.org/wp-content/uploads/2024/03/image.png546942Kim Stillhttps://aprovecho.org/wp-content/uploads/2015/11/Aprovecho-Logo.pngKim Still2024-03-15 16:14:532024-03-15 16:14:53From: EPA’s Lab Test Results for Household Cookstoves, Jim Jetter, 2012
Champion (2021) average energy emission factors (g/MJ) from ISO high, medium, and low tests.
Champion, Wyatt M., et al. “Cookstove Emissions and Performance Evaluation Using a New ISO Protocol and Comparison of Results with Previous Test Protocols.” Environmental Science & Technology, 2021, 55, (22), 15333-15342. DOI: 10.1021/acs.est.1c03390
Lab testing can quickly compare emissions from stoves. The EPA and ARC labs now measure the climate emission factors, not just PM2.5 and CO. It has been proven that only field tests show real world performance. Together, lab and field tests help to move stoves forward as we get closer to market driven stoves that please cooks, successfully cook food, use a lot less fuel, and protect health/climate.
The above chart contains a lot of information. Some takeaways are:
Wow! The Three Stone Fire (TSF) was pretty bad! 943g/MJ for PM2.5, 15.5 g/MJ for CO.
Charcoal made ~90% less PM2.5.
The Carbon Monoxide (CO) from charcoal was only a bit higher than the Three Stone Fire (19.2g/MJ).
LPG did so well! (Too bad that we are entering the end of the fossil fuel era).
The forced draft pellet stove looked great, as well. (PM2.5: 30g/MJ, 2.2g/MJ CO)
Black Carbon (EC) is much worse than CO2 for climate change. Many of the stoves, except the Rocket stove, successfully reduced Black Carbon.
R&D has shown that the Rocket stove requires successful forced draft mixing at high temperatures to decrease emissions of Black Carbon and potentially address climate.
When the emissions factors are summed and converted to global warming potential the forced draft stoves have the potential to generate large amounts of carbon offsets.
https://aprovecho.org/wp-content/uploads/2015/11/Aprovecho-Logo.png00Kim Stillhttps://aprovecho.org/wp-content/uploads/2015/11/Aprovecho-Logo.pngKim Still2024-02-09 16:07:592024-02-09 16:29:55Moving Forward: Thanks to Jim Jetter’s EPA Lab!
Dr. Sam Baldwin describes the use of a pot skirt in his book “Biomass Stoves: Engineering Design, Development, and Dissemination (1987).” Changes in the length and diameter of the channel gap (between the pot and the interior of the skirt) result in dramatic changes in heat transfer efficiency.
“In fact, the channel efficiency, defined as the fraction of the energy in the hot gas entering the channel that is transferred to the pot, is extremely sensitive to changes in the channel gap. For a 10cm long channel, the channel efficiency drops from 46% for an 8mm gap to 26% for a 10cm gap. Thus the stove and pot dimensions must be very precisely controlled.” (pg. 45)
If stoves are to be compared, these types of variables must be controlled. The use of a standard pot, or pots, without pot skirts will result in performance scores that are significantly reduced. If a pot skirt is used on testing pots it should be identical in all aspects. Again, the use of a standard pot(s) seems to be required.
https://aprovecho.org/wp-content/uploads/2023/12/12.29.23-pot-skirt.jpg11101408Kim Stillhttps://aprovecho.org/wp-content/uploads/2015/11/Aprovecho-Logo.pngKim Still2023-12-29 18:22:422023-12-29 18:22:43Pot Skirts – basic theory
